In general, an airbag is installed in an automobile in order to protect an occupant using cushioning force at the time of an accident.
The airbag is inflated and deployed when gas generated by an inflator flows into the airbag. The inflator generates the amount of gas larger than an internal volume of the airbag to sufficiently inflate the airbag.
Therefore, in a case in which the gas flowing into the airbag is not discharged, the airbag is excessively inflated, and for this reason, the occupant may be seriously injured due to excessive expansive pressure in the airbag when the occupant comes into contact with the airbag. To prevent the occupant from being injured due to the excessive expansive pressure in the airbag as described above, a vent hole through which the gas flowing into the airbag is discharged is formed in the airbag.
However, in a case in which an excessive large amount of gas is discharged through the vent hole, the airbag becomes excessively loosened, and for this reason, the airbag bounces and shakes a head of the occupant when the occupant comes into contact with the airbag, which causes an injury to a neck of the occupant.
As described above, the adjustment of the amount of gas discharged from the airbag has a great effect on safety of the occupant.